1. Field of the Invention
The present invention relates in general to a fluid-filled cylindrical elastic mount capable of isolating vibrations applied thereto, based on flows of a fluid contained therein. More particularly, the invention is concerned with such a fluid-filled elastic mount capable of exhibiting excellent isolating characteristics with respect to the vibrations applied in any radial direction perpendicular to the axis of the amount.
2. Discussion of the Prior Art
A cylindrical elastic mount is known as a device for elastically or flexibly connecting two members in a vibration system in a vibration damping or isolating manner. An example of such a cylindrical elastic mount is disclosed in laid-open Publication No. 48-310 of unexamined Japanese Utility Model Application. The cylindrical elastic mount disclosed in the publication has an inner and an outer metallic sleeve which are disposed in radially spaced-apart relation with each other. Between these inner and outer sleeves, there is interposed an elastic body for elastically connecting the two sleeves. The thus constructed elastic mount is adapted to isolate vibrations which are applied between the inner and outer sleeves primarily in radial directions perpendicular to the axis of the mount. The cylindrical elastic mount of the above type is widely used as a differential mount, engine mount, body mount or suspension bushing for a motor vehicle, for example.
To meet an increasing requirement for a higher degree of vibration isolating capability, a so-called fluid-filled elastic mount has been recently proposed, as disclosed in laid-open Publication No. 56-164242 of unexamined Japanese Patent Application and laid-open Publication No. 52-16554 of examined Japanese Patent Application. A fluid-filled elastic mount as disclosed in these publications has a pair of fluid chambers which are formed between the inner and outer sleeves, and are disposed opposite to each other in a diametric direction of the mount. The two fluid chambers are held in fluid communication with each other through a suitable orifice passage, so that vibrations applied to the mount may be effectively isolated by resonance of a fluid flowing through the orifice passage. The thus constructed fluid-filled elastic mount provides excellent vibration isolating characteristics, which have not been obtained by the above-described elastic mount that utilizes only elastic deformation of the elastic body for damping the input vibrations.
The conventional fluid-filled elastic mount having the orifice passage as described above is considerably complicated in construction, and therefore suffers from comparatively low production efficiency owing to the cumbersome process of assembling those components which define the orifice passage.
Further, the fluid contained in the fluid-filled elastic mount is forced to flow between the two fluid chambers, through the orifice passage, as a result of relative pressure changes between the two chambers, only when the elastic mount receives vibrations in the radial or diametric direction in which the two fluid chambers are opposed to each other. In other words, upon application of vibrations in the other radial directions of the mount, the elastic mount is incapable of providing a satisfactory effect of isolating the applied vibrations. Thus, it is rather difficult for the conventional fluid-filled elastic mount to provide a sufficient degree of isolating effect for the vibrations applied in all the radial directions perpendicular to the axis of the mount.
Even if vibrations are applied to the fluid-filled elastic mount in only one radial direction, the circumferential orientation of the mount upon installation on a motor vehicle, for example, must be attentively effected so that the direction in which the two fluid chambers are opposed to each other coincides with the radial direction in which the vibrations are applied to the mount, since the mount exhibits sufficient isolating characteristics only for the vibrations applied in that radial direction. Thus, cumbersome procedures and considerable attention are needed for the installation of the elastic mount.
Furthermore, the isolating characteristics based on the fluid flows in the conventional fluid-filled elastic mount are effective only for the vibrations in a relatively narrow frequency range in the vicinity of the resonance frequency of the fluid flowing through the orifice passage. Namely, it is extremely difficult for the conventional fluid-filled elastic mount to provide a sufficient isolating effect over a relatively wide frequency range of input vibrations.